1. Field of the Invention
The present invention relates to a fixing apparatus that fixes an unfixed image on a recording sheet by passing the recording sheet through a fixing nip, and an image formation apparatus that includes the fixing apparatus.
2. Related Art
In fixing apparatuses included in image formation apparatuses such as copiers, there is a so-called belt-nip system in which a fixing nip is secured by pressing a pressure belt against a fixing roller, and an unfixed image formed from toner or the like on a recording sheet is fixed thereon by passing the recording sheet between the pressure belt and the fixing roller (see Japanese Patent Application Publication No. 2005-300732).
In a belt-nip system fixing apparatus, a pressing member that presses the pressure belt towards the fixing roller is disposed on an inner face of the pressure belt, and the fixing nip is secured between the pressure belt and the fixing roller by the pressure. The pressure belt generally is driven to rotate by the driving rotation of the fixing roller. Interposing, for example, a low friction sheet for reducing friction between the pressure belt and the pressing member enables reducing the friction between the pressed portions.
However, the friction between the pressure belt and the pressing member cannot be completely eliminated even with use of the low friction sheet, and when the pressure belt, etc. erodes with the passage of time, thereby increasing the frictional force, the drive load on the pressure belt increases due to the frictional force.
When the drive load on the pressure belt increases, there is a brake effect on the driven pressure belt, though the fixing roller tries to continue rotation as usual. When a recording sheet having an unfixed toner image formed thereon passes between the fixing roller and the pressure belt, there are cases when image slippage occurs due to the toner image on the recording sheet shifting on the recording sheet as if sliding.
Conventionally, replacement of the pressure belt, etc., is performed frequently to prevent this type of image slippage occurring over time.